GENERIC AFFINITIES AND EVOLUTION
Kretzschmaria (also as Ustulina)
has been considered as closely allied to Xylaria,
based upon developmental and cytological studies and the morphology of the anamorph (Jong
and Rogers, 1972; Laessøe, 1994; Rogers, 1968; Tulasne and Tulasne, 1863). Interestingly,
Miller (1928) concluded that Kretzschmaria (as Ustulina)
developed in a manner consistent with the Hypoxylon
pattern and favored placement of U.
deusta in Hypoxylon. Ustulina deusta
was included in Millers monograph of Hypoxylon as H. deustum
(Miller, 1961). Millers concept of Hypoxylon, however, was much
broader than the currently prevalent view (see Ju and Rogers, 1996). Nilsson et al. (1989)
showed that seven Xylaria species caused both Type 1 decaycavity
formation typical of soft rot decayand Type 2 decay (see earlier), whereas K.
deusta (as H. deustum) caused only Type 2 decay.
It thus more closely resembled three Daldinia
Ces. & De Not. species and five Hypoxylon Bull. species in its decay
pattern than Xylaria!
Ustulina has traditionally been separated from Kretzschmaria based upon the stalked stromata of K. clavus, the type species of the latter genus. Cultures and teleomorphic structures, however, are so similar as to make such a separation unsupportable. Kretzschmaria is closely related to Nemania S. F. Gray as emended by Pouzar (1985a, 1985b) and, indeed, a case could be made for putting Kretzschmaria and Ustulina into synonymy with it. Nonetheless, Kretzschmaria is distinctly different from Nemania. The former genus produces conidiophores in dense palisades on immature stromata in nature and is known to produce the anamorph in culture in only a few instances. Cultures on OMA soon become furrowed and loosened from the plate. Nemania produces more or less loose, scattered conidiophores in nature and on culture plates; cultures are usually smooth and lack furrows.
Kretzschmaria curvirima, K. macrosperma, K. micropus, and probably K. cetrarioides apparently produce their anamorphs on synnemata rather than over the surface of the immature teleomorph. This indicates a relationship with Stilbohypoxylon Möller (see Rogers and Ju, 1997). Stilbohypoxylon itself, however, can be viewed as highly related to Xylaria or , indeed, a reduced Xylaria. Unfortunately, the above Kretzschmaria taxa have not been cultured. Future studies should tell whether the taxonomic arrangement used herein is tenable.
The kretzschmarioid and ustulinoid taxa, respectively, are remarkably similar. Indeed, a number of them seem to be members of a series morphologically distinguishable primarily on ascospore size. Future studies of more taxa in culturable condition might provide data that alter our current concepts of species in these fungi.